With the quantity of wireless communication devices that support Machine Type Communications (MTC) expected to dramatically increase in the near future, efforts are underway to mitigate core network and radio interface NAS signaling capacity limitations so as to maximize the number of system access attempts that can be successfully processed during periods of high system loading.
In a conventional packet switched wireless communication system, a wireless communication device may be configured to transmit NAS signaling messages to a core network node (e.g., a Serving General Packet Radio Service (GPRS) Support Node (SGSN)). When a wireless communication device sends a NAS signaling message targeted for an SGSN, such as, for example, a Routing Area (RA) Update message, a base station subsystem (BSS) will receive the NAS signaling message within the context of a Logical Link Control (LLC) Packet Data Unit (PDU), along with a Packet Flow Identifier (PFI) that indicates NAS “signaling” (i.e., PFI=1). The PFI is conveyed from the wireless communication device to the BSS either within a Radio Link Control (RLC) data block header, when a one-phase access is used, or within the Packet Resource Request message, when a two-phase access is used. Once received, the LLC PDU and its corresponding PFI are relayed from the BSS to the SGSN using, for example, a UL-UNITDATA PDU as specified in 3GPP Technical Specification 48.108. However, the PFI is limited to only indicating “signaling” for the case of NAS signaling, as indicated in 3GPP Technical Specification 24.008. As such, the SGSN cannot distinguish between NAS signaling scenarios that can be treated with low priority and NAS signaling scenarios that can be treated with normal priority. The result is a lost opportunity for mitigating core network and radio interface congestion.
In a conventional wireless communication system in the circuit switched (CS) domain, when a wireless communication device needs to send a NAS message targeted for the mobile switching center (MSC), such as, for example, a Location Area Update message, the wireless communication device first sends a Channel Request message to the BSS indicating “Location Updating.” The wireless communication device is subsequently sent an Immediate Assignment message that provides the wireless communication device with a Traffic Channel/Stand-Alone Dedicated Control Channel (TCH/SDCCH) resource allocation, which the wireless communication device uses to send a layer 3 service request message to the BSS. The layer 3 service request message consists of a LOCATION UPDATING REQUEST message carried within a layer 2 Set Asynchronous Balanced Mode (SABM) frame. Upon reception of the LOCATION UPDATING REQUEST message, the BSS relays it to the MSC within a COMPLETE LAYER 3 INFORMATION message. However, the layer 3 service request message sent from the MS to the BSS has no way of indicating a priority level associated with the corresponding LOCATION UPDATING REQUEST. As such, when this message is relayed to the MSC, the MSC has no way of knowing when a low priority LOCATION UPDATING REQUEST message has been received. The result is a lost opportunity for mitigating core network and radio interface congestion.